1. The Field of the Invention
The present invention relates to surgical instruments. More specifically, the present invention relates to thermally adjustable resecting loops used in open and minimally invasive surgical procedures and interventional surgical and therapeutic procedures.
2. State of the Art
Surgery generally involves cutting, repairing and/or removing tissue or other materials. These applications are generally performed by cutting tissue, fusing tissue, or tissue destruction.
Current electrosurgery modalities used for cutting, coagulating, desiccating, ablating, or fulgurating tissue, have undesirable side effects and drawbacks. For example, monopolar and bipolar electrosurgery modalities generally have disadvantages relating to “beyond the tip” effects. These effects are caused by intentionally passing alternating current through tissues in contact with conducting instruments or probes.
Monopolar surgical instruments require electric current to pass through the patient. A return electrode is placed on the patient, often on the patient's thigh. Electricity is conducted from a “knife” or “loop” electrode through the tissue and returns through the return electrode. Other forms of monopolar instruments exist, such as those which use the capacitive effect of the body to act as the return electrode or ground.
A low voltage high frequency waveform will incise, but has little hemostatic effect. A high voltage waveform will cause adjacent tissue hemostasis and coagulation. Therefore, when hemostasis is desirable, high voltage is used. The high voltage spark frequently has deeper tissue effects than the cut because the electricity must pass through the patient. The damage to the tissue extends away from the actual point of coagulation. Furthermore, there are complaints of return electrode burns. Yet, any reduction of voltage reduces the effectiveness of hemostasis. Further, the temperature of the spark or arc cannot be precisely controlled, which can lead to undesirable charring of target tissue.
Bipolar surgical instruments can produce tissue damage and problems similar to monopolar devices, such as sparking, charring, deeper tissue effects and electric current damage away from the application of energy with varying effects due to the difference in electrical conductivity of tissue types, such as nerve, muscle, fat and bone, and into adjacent tissues of the patient. However, the current is more, but not completely, contained between the bipolar electrodes. These electrodes are also generally more expensive because there are at least two precision electrodes that must be fabricated instead of the one monopolar electrode.
Electrocautery resistive heating elements reduce the drawbacks associated with charring and deeper tissue damage caused by other electrosurgery methods. However, such devices often present other tradeoffs, such as the latency in controlling heating and cooling time, and effective power delivery. Many resistive heating elements have slow heating and cooling times, which makes it difficult for the surgeon to work through or around tissue without causing incidental damage. Additionally, tissue destruction with resistively heated tools can produce unintended collateral tissue damage.
Tissue destruction instruments generally heat tissue to a predetermined temperature for a period of time to kill or ablate the tissue. In some controlled heating of tissues, a laser is directed to an absorptive cap to reach and maintain a predetermined temperature for a predetermined amount of time. While this provides the benefits of thermal heating, it is expensive due to the complexity and expense of laser hardware.
In another tissue destruction procedure, a microwave antenna array is inserted into the tissue. These arrays are powered by instruments that cause microwave energy to enter and heat the tissue. While such devices are often effective at killing or ablating the desired tissue, they often cause deeper tissue effects than the desired area. Additionally the procedures can require expensive equipment.
Uses of ferrite beads and alloy mixes in ceramics have been examined as an alternative to other tissue destruction methods. When excited by the magnetic field associated with high frequency current passing through a conductor, ferrite beads and alloy mixes in ceramics can reach high temperatures very quickly. However, one major problem with the use of these materials is that a large temperature differential can cause the material to fracture, especially when it comes into and out of contact with liquids. In other words, if a hot ferrite surgical instrument is quenched by a cooler pool of liquid, such as blood or other body fluids, the material's corresponding temperature drops rapidly and may cause the material to fracture. These fractures not only cause the tool to lose its effectiveness as a heat source, because the magnetic field is disrupted, but may require extraction of the material from the patient. Obviously, the need to extract small pieces of ferrite product from a patient is highly undesirable.
In addition, removing tissue can be complicated. Removal of tissue with a blade may require several incisions or a delicate hand with complicated movements. Furthermore, access to a tumor may be from an angle perpendicular to the tissue. There may be little room to maneuver a blade and its handpiece to the side. This can make resecting a piece of tissue more difficult than simply cutting through tissue. Alternatively, lasers or bipolar forceps can be employed to produce heat to dessicate the surface of the target tissue, which can then be removed with forceps, and then the heat applied again in order to remove the next layer of tissue if necessary. This process can be tedious and produce unwanted bleeding that may obscure vision, complicate the surgery and jeopardize the well-being of the patient.
Thus, there is a need for an improved thermal surgical tool to remove tissue.